Currently, relay techniques are gradually adopted in wireless communication technology to improve wireless communication coverage area, group mobility, cell-edge throughput of base stations and provision of temporary network deployment. For example, IEEE 802.16m standard and Third Generation Partnership Project Long Term Evolution Advanced (3GPP LTE-Advanced) standard both adopt replay node (also called a relay station) for achieving the relay forwarding communication.
FIG. 1 is a schematic diagram of a wireless communication system 19 with a relay node. As shown in FIG. 1, the wireless communication system 10 supports 3GPP LTE standard, and includes a mobility management entity (MME) 112, an MME 114, an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 120 and user equipments (UE) 132, 134, 136. The MME 112 can also be integrated with a serving gateway (S-GW).
The E-UTRAN 120 can include an enhanced Node B (eNodeB or abbreviated as eNB) 122, an eNB 124 and a relay node 126. The E-UTRAN 120 is connected with MME/S-GW 112 via an S1 connection (interface). In the E-UTRAN 120, the eNB 122 and the eNB 124 are connected with each other via an X2 interface (which can be a wired communication). In the wireless communication system 10, the relay node 126 can be connected with the eNB 124 via the X2 interface. However, the relay node 126 can also be connected with a base station or an advanced base station (abbreviated as ABS), in order to establish an S1 interface with the MME/S-GW 112. The relay node 126 provides a Uu interface (not shown) for the UE 134, 136, so as to provide wireless communication service of the eNB 124 to the UE 134, 136. The UE 132 is directly connected with the eNB 122 without via the relay node 126.
In the wireless relay communication system supporting 3GPP LTE standard, such as in the wireless communication system 10, the relay node 126 may not have a base station ID (cell ID), such that the relay node 126 does not create a new cell, but it can still relay or forward data to the UE 134, or forward data to the UE 134 from the eNB 124. The UE 134 may just receive control signals from the eNB 124, such as Physical Downlink Control Channel (PDCCH) or cell reference signal. The UE 134 can receive data signals from the relay node 126, such as Physical Downlink Shared Channel (PDSCH). Moreover, in the wireless communication system 10, the relay node can transmit or receive wireless signals in an uplink band or a downlink band of the eNB 124 in a time division multiplexing (TDM) mode, so as to extend wireless service coverage area of the eNB 124. In some situations, the relay node 126 just supports relaying data, and the eNB 124 and the UE 134 exchange physical (PHY) data.
FIG. 2A is a schematic diagram illustrating a conventional HARQ process in a downlink transmission of a frequency division duplex (FDD) mode of LTE system. Each block in FIG. 2A denotes a plurality of subframes. In 3GPP LTE standard, each frame includes 10 subframes. The figure shown in each block denotes a timing sequence of every subframe. For example, a subframe “n+3” represents the 3rd subframe appeared after the nth subframe, and such notation principle can be applied to following schematic diagrams of every HARQ process. Referring to FIG. 2A, the HARQ process is operated between a base station (e.g., the eNB 122) and a mobile communication device (e.g., the UE 132). The blocks shown in the top row represent the subframe timing sequence of the base station, and the blocks shown in the bottom row represent the subframe timing sequence of the mobile communication device.
As illustrated in FIG. 2A, wireless resource is allocated for the eNB 122 in the subframe “n+6” and the eNB 122 transmits PDCCH and PDSCH to the UE 132. After 4 subframes, the subframe “n+10”, the IE 132 replies a positive acknowledgement (abbreviated as ACK)/a negative acknowledgement (abbreviated as NACK), and feedback to the eNB 122 whether the HARQ data is successfully received in the subframe “n+6”. The aforementioned 4 subframe interval is a configured and fixed time interval defined in 3GPP LTE standard. If the eNB 122 receives the ACK, then the eNB 122 can prepare another HARQ process. On the contrary, if the eNB 122 receives the NACK, then the eNB 122 can arrange retransmission explicitly or implicitly in subsequent subframes. For example, the eNB 122 can arrange the UE 132 report the reception result after 4 subframes, and the eNB 122 can arrange downlink resource for retransmitting the HARQ data in an explicit arrangement example. In an implicit arrangement example, fixed timing is reused for retransmitting the HARQ data to the UE 132 until the eNB 122 receives an ACK feedback from the UE 132. Alternatively, a preset timeout can be used to terminate the retransmission of the HARQ data.
FIG. 2B is a schematic diagram illustrating a conventional HARQ process in an uplink transmission of an FDD mode of LTE system. Referring to FIG. 2B, before an uplink transmission process of the UE 132, the eNB 122 grants uplink resource to the UE 132 in subframe “n”, which is allocated through control signaling such as PDCCH. After 4 subframes, the UE 132 transmits uplink data to the eNB 122 in the granted subframe “n+4” through, for example, a Physical Uplink Shared Channel (PUSCH). Once the eNB 122 receives the uplink data, after 4 subframes, the eNB 122 replies an ACK signal to feedback whether the uplink data is successfully received in subframe “n+8”. If the uplink data transmission is failed, the eNB 122 can reply an NACK signal or a fake-ACK signal in the subframe “n+8”, which is 4 subframes after the uplink data transmission. Alternatively, the retransmission is triggered in a fixed subframe (e.g., J subframes), and the J value can be assigned explicitly or implicitly.
FIG. 3A is a schematic diagram illustrating a category of frame structures of a time division duplex (TDD) in LTE system. FIG. 3A illustrates a look-up table, which further indicates 7 uplink/downlink (UL/DL) configurations of the TDD mode in 3GPP LTE system, such as a configuration 0 to a configuration 6. Different configurations may have an uplink-to-downlink (UL-to-DL) switchpoint periodicity of 5 microseconds (ms) or of 10 ms. The UL-to-DL switchpoint periodicity represents a repeating time interval of the configured frame structure. Moreover, the loop-up table further shows corresponding uplink transmission meaning or corresponding downlink transmission meaning of 10 subframes in each UL/DL configuration. Each subframe occupies 1 microseconds of wireless resource in time domain. Furthermore, the subframe labeled as “D” or “S” represents a downlink transmission, and the subframe labeled as “U” represents an uplink transmission. For example, as shown in FIG. 3A, in a configuration 0, the subframes 0, 1, 5, 6 are allocated for the downlink transmission while the subframes 2, 3, 4, 7, 8, 9 are allocated for the uplink transmission.
FIG. 3B is a schematic diagram illustrating a mapping of downlink data subframe allocated in a TDD mode of LTE system and corresponding ACK/NACK. The example shown in FIG. 3B corresponds to an uplink transmission example similar to that shown in FIG. 2A, but the differences between them lies in that FIG. 3B provides a configuration table converted from the look-up table of FIG. 3A. Moreover, the configuration table shows the timing association of subframes transmitting ACK/NACK and subframes transmitting data created due to the TDD frame structure. The configuration tale also provides the associations of the subframes transmitting ACK/NACK and subframes transmitting data in the HARQ transmission process, where the figures shown in the block is the value of k.
In examples of FIG. 3B, if the eNB 122 transmits downlink data in the subframe “n−k”, then the mapping table shows that the subframe “n” is granted by the eNB 122 for transmitting data or ACK/NACK. For example, in configuration 1 (also in a situation of UL-DL switchpoint periodicity of 5 ms), if the UE 132 replies ACK/NACK in the subframe 2, then it can be known by looking up in the configuration table of FIG. 3B, the UE 132 received the downlink data in the subframe 5 (i.e., n−k=(2−7)+10=5) or in the subframe 6 (i.e., n−k=(2−6)+10=6). For another example, in configuration 4, if the UE 132 replies ACK/NACK in the subframe 2, then it can be known by looking up in the configuration table of FIG. 3B, the UE 132 received the downlink data in the subframe 0 (i.e., n−k=(2−12)+10=0), the subframe 4 (i.e., n−k=(2−8)+10=4), the subframe 5 (i.e., n−k=(2−7)+10=5) or in the subframe 1 (i.e., n−k=(2−11)+10=1).
FIG. 3C is a schematic diagram illustrating associations of subframes in every configuration of FIG. 3B. In the mapping table shown in FIG. 3C, the subframe labelled as “D” may be associated with the subframe labelled as “A”. For example, in configuration 1, when the subframe “n” is 2, the subframe 2 labelled as “A” is then associated with the subframes 5, 6, which are labelled as “D”. For another example, in configuration 4, when the subframe “n” is 2, the subframe 2 labelled as “A” is then associated with the subframes 0, 1, 4, 5, which are labelled as “D”. In other words, when the eNB 122 transmits downlink data in the subframes 0, 1, 4 or 5 in the configuration 4, the UE 132 can reply ACK/NACK signal in the subframe 2 of the next frame period.
The uplink HARQ process in the TDD mode of 3GPP LTE system is similar to the process shown in FIG. 2B, but the difference between then lies in that a timing associations between grant subframes, uplink data subframes and ACK/NACK subframes are required due to the TDD frame structure. FIG. 4A is a schematic diagram illustrating a mapping of grant subframe allocated in a TDD mode of LTE system and corresponding uplink data subframe. FIG. 4A corresponds to an uplink HARQ data transmission example similar to that shown in FIG. 2B. As shown in FIG. 4A, if grant signal is transmitted in the subframe “n”, then the UE can transmits the uplink data in the subframe “n+k”. For example, in the configuration 1, if the eNB 122 transmits the grant signal in the subframe 1, then the UE can transmits the uplink data in the subframe 7 (i.e., n+k=1+6=7).
FIG. 4B is a schematic diagram illustrating a mapping of uplink data subframe allocated in a TDD mode of LTE system and corresponding ACK/NACK. FIG. 4B corresponds to an uplink HARQ transmission example similar to that shown in FIG. 2B, and shows timing associations of uplink subframes and the corresponding ACK/NACK subframes as following FIG. 4A. As shown in FIG. 4B, if uplink data is transmitted in the subframe “n”, then the eNB 122 can transmit ACK/NACK signal in the subframe “n+k”. For example, in configuration 1, if the UE 132 transmits the uplink data in the subframe 7, then the eNB 122 can transmit ACK/NACK in the subframe 1 (i.e., n+k=7+4−10=1) in the next frame period.
FIG. 4C is a schematic diagram illustrating associations of subframes in every configuration of FIG. 4B. FIG. 4c corresponds to an uplink HARQ data transmission example similar to that shown in FIG. 2B, and provides a configuration table converted from FIG. 4A and FIG. 4B. In the configuration table of FIG. 4C, the subframe labelled as “G” is represents a time point of transmitting the grant signal for the subframe labelled as “D”, and the subframe “A” is represents a time point of transmitting ACK/NACK signal for the subframe labelled as “D”. For example, if configuration is 0, and in the situation where subframe n=1, the eNB 122 transmits grant signal in the subframe 1, and the UE 132 can transmit uplink data in the subframe 7, and the eNB 122 can transmit the ACK/NACK signal in the subframe 1 of the next frame period. For another example, if configuration is 5, and in the situation where subframe n=8, the eNB 122 transmits grant signal in the subframe 8, and the UE 132 can transmit uplink data in the subframe 2, and the eNB 122 can transmit the ACK/NACK signal in the subframe 8 of the next frame period.
However, the aforementioned conventional HARQ method, as illustrated in FIG. 2A and FIG. 4B, can merely be applied to the situation without a relay node. Moreover, the conventional wireless relay communication system mostly uses dynamic allocation indication signals, which results in control signalling overhead in the wireless relay communication system. The dynamic allocation indication signalling is also more complicated, and can easily lower operation efficiency of the entire wireless relay communication system. Therefore, how to efficiently transmit data and corresponding control signals in a wireless relay communication system is currently an important issue.